The present invention relates to a method and device for determining a driving torque correction factor for compensating and/or for balancing the cooperating driving torques of different drive devices (and/or of driving torques acting on a common drive shaft).
There already exists a wide variety of drive units for motor vehicles, which exhibit two or more drive devices for generating a (total) driving torque, acting on a common drive shaft. In particular, hybrid vehicles, which are constructed in accordance with a so-called parallel hybrid system, usually exhibit an internal combustion engine and an electric motor. In this case their individual driving torques are added together to form a common total driving torque. The coordination of such drive units is usually accomplished by a drive management and consists in essence of model-based torque inputs of a control unit to the internal combustion engine and the electric motor.
An object of the invention is to provide a method for a drive unit with two individual drive devices that act with their individual driving torques on a common drive shaft. According to the invention, irregularities caused by a change in the torque distribution of the individual torques between the individual drive devices for maintaining a resulting total torque shall be reduced or even eliminated.
The invention is based on the knowledge that when drive units with different drive devices for generating individual driving torques (which act on a common drive shaft and/or which add up to a total driving torque (for example, a parallel hybrid system)) are operating, a different conversion ratio of the torque requirement (by the different drive devices) may result in a deviation of the driving torque, which is to be adjusted because of the load demand, and, thus, may result in an undesired bucking in the common drive train during a changeover between the drive units, during which the one drive unit takes over for the other drive device at least to some extent the load torque demanded. In other words, the (torque) difference between the different drive devices (the reason for the difference in day-to-day operation being based on a control for determining the torque distribution between the internal combustion engine and the electric motor or on the basis of module tolerances and production tolerances and on the basis of wear and tear) shall be equalized during the conversion of the desired values to the actual values (i.e., during the conversion of a desired driving torque to an actual driving torque) by means of a compensating method according to the invention. To this end the compensating method may be carried out after the production of such a drive unit (including two different drive devices) and/or after the production of a hybrid vehicle with such a drive unit and optionally even after the passage of a defined operating period of the drive unit.
This object is achieved by exemplary embodiments according to the present invention.
The first step in carrying out the inventive methods is to specify a desired driving torque for one of the two drive devices and then to adjust a brake torque, which acts against the specified desired driving torque, by means of the other drive device.
According to one exemplary embodiment, the setting of the brake torque takes place in a regulated manner in that the brake torque is adjusted as far as to a value that is equivalent to the value of the actual driving torque, which occurs owing to the specified desired driving torque. As soon as this torque uniformity has been set, no additional change in the speed of the common drive shaft will take place. The driving torques and/or the brake torques that were specified and/or set in this period of time are determined; and a correction value is determined as a function of the determined torques. The correction value may be calculated from the ratio of the specified desired torque to the adjusted brake torque at the time of the torque compensation.
According to another exemplary embodiment, the setting of the brake torque takes place in an unregulated manner in that only the desired driving torque of the one drive device is put opposite a predefined (known) brake driving torque of the other drive device; and subsequently the change in speed (speed gradient) that occurs in the common drive shaft is determined; and a correction value is determined as a function of this change in speed. In this case, when the correction value is determined, not only the speed gradient but also the masses of both drive units, which are to be put into motion (to be rotated), as well as optionally the specified desired driving torque and the adjusted known brake torque may be taken into consideration.
In both of the above described embodiments the correction value is determined uniformly for all operating points by determining just once a correction value at only one operating point or by determining individually the correction values for a plurality of operating points in order to prepare a correction value family of characteristics.
In each case the correction factor is determined advantageously as a function of the variables that influence the driving torque of at least one of the two different types of drive devices (internal combustion engine/electric motor). In particular, such variables as the ambient air pressure, the ambient temperature, the temperature of the internal combustion engine, the temperature of the electric motor, the temperature of the energy accumulator supplying the electric motor, are included in the process of determining the correction factor.
In a subsequent operation of the drive unit with its two different (individual) drive devices, this correction value and/or this correction value family of characteristics may always be used to specify the torque for the different (individual) drive devices. Taking into consideration the correction value, these torque inputs are also fulfilled with identical driving torque values.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.